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Neal
Neal, Chevy Mechanic
Category: Chevy
Satisfied Customers: 8351
Experience:  Shop Owner and Mechanic on multiple makes.
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CHEVROLET PRIZM: CHECK ENGINE CODE THE CODE is p0420 I WAS WANTING

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I HAVE A CHEVROLET PRIZM WITH A 4 CYL. ENGINE AND I HAVE A CHECK ENGINE CODE THE CODE IS P0420 I WAS WANTING TO KNOW WHAT CAUSES THAT CODE AND WHAT SHOULD I DO TO FIX IT.

I'm Neal and I am here to assist you. Only accept when you are happy with my assistance. If I can't help I will open your Question to other experts.

 

The catalytic converter has an oxygen sensor in front and behind it. Typically the code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of a converter that is not working as efficiently as it should be.

 

That code may mean that one or more of the following has happened:

  • An oxygen sensor is not reading (functioning) properly
  • The engine coolant temperature sensor is not working properly
  • Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
  • Retarded spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings

Some suggested steps for troubleshooting:

  • Check for exhaust leaks at the manifold, pipes, and catalytic converter.
  • Inspect the downstream heated oxygen sensor (HO2), replace if necessary
  • Replace the catalytic converter

 

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